Fuel tank venting control valve assembly

ABSTRACT

A tank pressure control valve is provided for controlling the discharge of fuel vapor from a fuel tank. In one embodiment, the tank pressure control valve is configured to use pressurized fuel vapor to control a flexible diaphragm operable between a closed position blocking discharge of fuel vapor from the fuel tank and an opened position allowing such discharge. In another embodiment, the tank pressure control valve is configured to use pressurized fuel vapor to move a flexible diaphragm to move a rigid valve member between a closed position and an opened position.

BACKGROUND AND SUMMARY OF THE INVENTION

This application is a continuation-in-part of co-pending patentapplication Ser. No. 07/328,451, filed Mar. 24, 1989 now U.S. Pat. No.4,953,583.

The present invention relates to fuel tank pressure control valves forselectively discharging pressurized fuel vapor from a fuel tank. Moreparticularly, the invention relates to fuel tank pressure control valvesdesigned to maintain a predetermined vapor pressure in the fuel tankduring refueling to prevent a pump nozzle operator from overfilling thefuel tank and to vent pressurized fuel vapor from the fuel tank, whennecessary, after the tank has been refueled.

Although fuel pump nozzles are known to include sensor means forshutting off the flow of fuel from the nozzle when the fuel tank isnearly filled, it has been observed that users frequently manuallyoverride or bypass such fill-limiting sensors by continuing to pump fuelafter the pump nozzle has automatically shut off several times. It willbe appreciated that such unauthorized refueling practices can result inoverfilling the fuel tank which can effectively reduce the fuel vaporexpansion capacity available within the filled fuel tank.

An improved fuel vapor control valve is provided for maintaining a headpressure within the fuel tank which exceeds the maximum head pressurethat can develop in the filler neck due to filling the filler neck withfuel. The improved valve advantageously aids in preventing fuel pumpoperators from overfilling fuel tanks by providing a pressurized fuelvapor barrier within the fuel tank that acts to block the introductionof fuel into the fuel tank in excess of a predetermined fuel capacityduring refueling. At the same time, the improved valve is adaptedautomatically to open and release pressurized fuel vapor after refuelingto increase the flow of fuel vapor to a fuel vapor treatment site and/orthe atmosphere, thereby enhancing engine performance, and avoidingshortcomings of known fuel tank valves.

One object of the present invention is to provide a tank pressurecontrol valve that closes automatically during refueling to retain fuelvapor in the fuel tank to develop a pressure head in the tank andprevent overfilling of the tank and yet also opens automatically to ventfuel vapor from the fuel tank at all other times should the pressure ofthe fuel vapor in the fuel tank rise above a predetermined level.

Another object of the present invention is to provide a tank pressurecontrol valve of small size having a high discharge capacity to vent thefuel tank properly while the vehicle is stationary or operating.

Yet another object of the present invention is to vent high pressurefuel vapor from the fuel tank using one or more differential pressurevalve assemblies that move between opened and closed positions inresponse to changing vapor pressures in the fuel tank or filler neck.

Another object of the present invention is to provide a tank pressurecontrol valve assembly configured to use fuel vapor pressure to controla flexible diaphragm operable between a closed position blockingdischarge of fuel vapor from the fuel tank and opened positions allowingsuch discharge.

Still another object of the present invention is to provide a tankpressure control valve assembly configured to use fuel vapor pressure tocontrol a flexible diaphragm positioned to actuate a separate vent valveoperable between a closed position blocking discharge of fuel vapor fromthe fuel tank and opened positions allowing such discharge.

According to the present invention, an apparatus is provided forcontrolling discharge of fuel vapor from a fuel tank having a fillerneck. The apparatus includes means for conducting fuel vapor between thefuel tank and a fuel vapor treatment site and means for selectivelyblocking flow of fuel vapor through the conducting means. The blockingmeans is operable between a flow blocking position blocking flow of fuelvapor through the conducting means and flow delivery positions allowingfuel vapor to flow through the conducting means. In addition, theapparatus includes means for delivering fuel vapor to the blocking meansto apply a closing pressure to the blocking means and means for usingpressurized fuel vapor in the filler neck to selectively block flow offuel vapor through the delivery means. Thus, the using means controlsdelivery of pressurized fuel vapor to the blocking means to control themovement of the blocking means between the flow-blocking position andflow-delivery positions.

In preferred embodiments, the blocking means comprises a diaphragmassembly. Thus, fuel vapor from the fuel tank delivered through thedelivery means acts against the diaphragm assembly to control dischargeof fuel vapor through the conducting means.

In alternative embodiments of the present invention, an apparatus isprovided for controlling discharge of fuel vapors from a fuel tankhaving a filler neck. The apparatus comprises means for conducting fuelvapor between the fuel tank and a fuel vapor treatment site, means forselectively blocking flow of fuel vapor through the conducting means,and means for actuating the blocking means in response to development offuel vapor pressure in the filler neck. The blocking means is disposedin the conducting means and is operable between a flow-blocking positionblocking flow of fuel vapor through the conducting means andflow-delivery positions allowing fuel vapor to flow through theconducting means. The actuating means operates to move the blockingmeans away from its flow-blocking position toward a flow deliveryposition when the pressure of fuel vapor in the filler neck exceeds apredetermined level. Thus, when the pressure of fuel vapor in the fillerneck rises beyond the predetermined level, the actuation means moves theblocking means to allow fuel vapor to vent from the fuel tank throughthe conducting means to a fuel vapor treatment site.

In preferred embodiments the actuating means includes a diaphragmassembly deformable under the pressure of fuel vapor in the filler neckto bear against the blocking means to move it to a flow-deliveryposition. The blocking means can include, for example, a rigid valvemember.

Additional objects, features, and advantages of the invention willbecome apparent to those skilled in the art upon consideration of thefollowing detailed description of preferred embodiments exemplifying thebest mode of carrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a schematic of an embodiment of a valve assembly in accordancewith the present invention showing the valve assembly during refueling;

FIG. 2 is a schematic of the valve of FIG. 1 showing the valve assemblyafter the cap is reattached to the filler neck following refueling;

FIG. 3 is a schematic of another embodiment of a valve assembly inaccordance with the present invention showing the blocking means in itsflow-blocking position during refueling;

FIG. 4 is a schematic of the valve assembly of FIG. 3 showing blockingmeans in its flow-delivery position during vehicle operation; and

FIG. 5 is a schematic of yet another embodiment of the invention showingthe blocking means in its flow-blocking position during refueling.

DETAILED DESCRIPTION OF THE DRAWINGS

A schematic illustration of one embodiment of a fuel vapor control valve10 in accordance with the present invention is provided in FIGS. 1-2.Valve 10 is shown in FIGS. 1-2 to include a valve housing 11 connectedto a fuel tank 15 and defining an interior region 12. Valve housing 11can be mounted directly in a fuel tank 15 or can be connected in fluidcommunication with the fuel tank 15 by way of a conduit. Optionally, arollover valve assembly (not shown) can be interposed in the conduitbetween the fuel tank and valve housing 11.

A tube providing a fuel vapor conducting passageway 14 extends into theinterior region 12 to conduct fuel vapor between the fuel tank and theinterior region 12. Conducting passageway 14 includes an inlet aperture16 in communication with the fuel tank 15. Conducting passageway 14 alsoincludes a branch passageway 18 terminating in a first outlet aperture20. Branch passageway 18 serves as means for delivering an amount offuel vapor to the interior region 12 through first outlet aperture 20.

Conducting passageway 14 also includes a second outlet aperture 22. Fuelvapor flowing through conducting passageway 14 and then through secondoutlet aperture 22 during vehicle operation passes to an exit passageway24 as shown in FIG. 2. Advantageously, exit passageway 24 is connectedto a fuel vapor treatment apparatus, which may comprise, for example, acharcoal canister.

A flexible, annular diaphragm 26 having a first side 28 and a secondside 30 and being operable between a flow-blocking position andflow-delivery positions is mounted to housing 11 in interior region 12by conventional mounting means 32. Diaphragm 26 is positioned tosealingly engage a valve seat bordering first outlet aperture 20 toselectively block flow of fuel vapor through outlet aperture 20 ofbranch passageway 18. A spring 34 or other suitable biasing means isprovided to bias diaphragm 26 toward its flow-blocking position blockingflow of fuel vapor through outlet aperture 20 of branch passageway 18.Spring 34 seats against an interior wall 36 of housing 11 and actsbetween the interior wall 36 and the diaphragm 26.

Advantageously, diaphragm 26 cooperates with interior wall 36 to definea vapor flow channel 38. Vapor flow channel 38 lies in fluidcommunication with an inlet passageway 40 which in turn is positioned toreceive fuel vapor from filler neck 42 of the fuel tank. Filler neck 42is shown schematically in FIGS. 1-2 to be connected in fluidcommunication with the fuel tank 15. Thus, fuel vapor from the fuel tank15 flows to filler neck 42 and passes to the inlet passageway 40,subsequently flowing to the vapor flow channel 38 to supply a pressureto second side 30 of diaphragm 26.

When diaphragm 26 is moved to a flow-delivery position (shown in FIG.1), fuel vapor can flow through aperture 20 of branch passageway 18 intointerior region 12. Advantageously, fuel vapor in interior region 12 isdirected to act against a second flexible, annular diaphragm 44.Diaphragm 44 includes a first side 46 and a second side 48 and ismounted to housing 11 in interior region 12 by conventional mountingmeans 50. Diaphragm 44 is operable between a flow-blocking position andflow-delivery positions. Diaphragm 44 is positioned to sealingly engagea valve seat bordering outlet aperture 22 of conducting passageway 14 toselectively block flow of fuel vapor therethrough. A spring 52 seatedagainst an interior wall 54 of housing 11 acts to bias the diaphragm 44toward its flow-blocking position in cooperation with the pressurizedfuel vapor in interior region 12.

A bleed passageway 56 interconnects interior region 12 and exitpassageway 24 in fluid communication. Advantageously, when seconddiaphragm 44 is moved from its flow-blocking position towards aflow-delivery position during development of high fuel vapor pressure inthe fuel tank, pressurized fuel vapor entrapped in the interior region12 is forced through bleed passageway 56, thus gradually dissipating thepressure in interior region 12. Importantly, bleed passageway 56 issmall enough so as not to affect the buildup of pressurized fuel vaporinto the interior region 12 to move the diaphragm 44 to itsflow-blocking position as is desired during refueling of the fuel tank.When diaphragm 44 is moved to its flow-delivery position (shown in FIG.2), fuel vapor can flow through outlet aperture 22 of conductingpassageway 14 into exit passageway 24, eventually passing to a fuelvapor treatment site.

The operation of valve 10 during refueling is illustrated in FIG. 1. InFIG. 1, the filler neck 42 is uncapped for refueling and so is exposedto atmospheric pressure. Any pressurized fuel vapor in filler neck 42would normally be exhausted to the atmosphere through the open mouth offiller neck 42 instead of being conducted to the first side 28 of thediaphragm 26. Thus, inlet passageway 40 is also exposed to atmosphericpressure, as is vapor flow channel 38. Thus, as explained above, thefirst side 28 of diaphragm 26 is exposed to atmospheric pressure.

However, the second side 30 of diaphragm 26 is exposed to the pressureof the fuel vapor in the fuel tank 15 since pressurized fuel vapor isfree to flow through inlet aperture 16 of conducting passageway 14 andthen through branch passageway 18 to reach second side 30. When thepressure of fuel vapor in branch passageway 18 exceeds a predeterminedlevel, the diaphragm 26 is moved in opposition to the closing forces ofthe spring 34 and the generally atmospheric pressure in vapor flowchannel 38 away from its flow-blocking position toward a flow-deliveryposition, thereby allowing pressurized fuel vapor to escape from branchpassageway 18 through outlet aperture 20 into interior region 12 asillustrated by the arrows in FIG. 1.

Once the pressurized fuel vapor enters interior region 12, it supplies aforce against first side 46 of diaphragm 44 that is added to the closingforce provided by spring 52. Pressurized fuel vapor from the fuel tank15 flows through conducting passageway 14 to outlet aperture 22 to applya force against a portion of second side 48 of diaphragm 44 defined bythe area of outlet aperture 22. As shown, the area of first side 46 isproportionately larger than the area of that portion of side 48 exposedto aperture 22. Thus, while essentially the same fuel vapor pressure issupplied to both the first side 46 and the second side 48 of thediaphragm 44, the pressure acting against side 46 acts across aproportionately larger area than does the pressure acting across theportion of side 48. A proportionately greater force is thus exertedagainst side 46. Thus, diaphragm 44 remains in the flow-blockingposition as shown.

Advantageously, when diaphragm 44 is maintained in the flow-blockingposition, the pressurized fuel vapor is prevented from dischargingthrough aperture 22 and thus accumulates in the fuel tank 15 to providea fuel vapor barrier. The fuel vapor barrier occupies a given volume ofthe fuel tank 15 and thus limits the amount of liquid fuel which can beintroduced into the fuel tank during refueling. Thus, valve 10 operatesto assist in preventing overfilling of the fuel tank.

Operation of the valve 10 during operation of the vehicle is illustratedin FIG. 2. During vehicle operation the filler neck 42 is capped. Thus,pressurized fuel vapor in the fuel tank 15 can travel up the filler neck42 to inlet passageway 40 and then to vapor flow channel 38 where itexerts a force against first side 28 of diaphragm 26. The cap is inplace at all times other than refueling to permit pressurized fuel vaporto travel through vapor flow channel 38 to reach the first side 28 ofdiaphragm 26 without venting to the atmosphere through the mouth of thefiller neck 12.

Second side 30 of diaphragm 26 is also exposed to pressurized fuel vaporfor the fuel tank 15. Pressurized fuel vapor travels through branchpassageway 18 to reach second side 30 of diaphragm 26. Of course,pressurized fuel vapor in branch passageway 18 can only act against thatportion of side 30 lying within the area defined by aperture 20, whilepressurized fuel vapor in vapor flow channel 38 acts across the entirearea of side 28. Thus, despite the fact that diaphragm 26 is exposedsubstantially to equal fuel vapor pressures on both sides 28 and 30, thefuel vapor pressure acting across side 28 acts across a proportionatelylarger area than does the pressure acting across side 30 and is combinedwith the closing force of spring 34. It follows that a proportionatelylarger force is supplied to side 28, thus maintaining diaphragm 26 in aflow-blocking position blocking flow of fuel vapor through outletaperture 20 of branch passageway 18 into interior region 12 as long asthe fuel cap is in place on the filler neck 42.

Because fuel vapor is unable to flow to interior region 12, first side46 of diaphragm 44 is exposed only to essentially atmospheric pressure.However, second side 48 of diaphragm 44 is exposed to pressurized fuelvapor flowing in conducting passageway 14. When the pressure of thisfuel vapor reaches a predetermined level sufficient to overcome thebiasing force of spring 52, diaphragm 44 will move to a flow-deliveryposition allowing flow of pressurized fuel vapor through outlet aperture22 of conducting passageway 14 to exit passageway 24 and then to thefuel vapor treatment site. In this fashion, fuel vapors creatingexcessively high tank pressure can be vented either while the vehicle isstationary or running. Eventually tank pressure is reduced sufficientlythat spring 52 moves diaphragm 44 back to its flow-blocking position.

Another embodiment of a tank pressure control valve in accordance withthe present invention is provided in FIGS. 3-4. A tank pressure controlvalve 110 is shown to include a valve housing 112 connected to a fueltank having a filler neck 117. Valve housing 112 can either be mounteddirectly to the fuel tank or can be connected to the fuel tank 15 by wayof a conduit optionally containing a rollover valve assembly (not shown)therein. Valve housing 112 is formed to include a first vapor inletpassageway 114 open to communicate with the fuel tank 15. Valve housing112 is also formed to include a second vapor inlet passageway 116 incommunication with the filler neck 117 and a first vapor outletpassageway 118 in communication with a vapor treatment site. Vapor inletpassageway 116 can be opened to the atmosphere by removal of the fuelcap attached to filler neck 117 as shown in FIG. 4.

A flexible, annular diaphragm 120 is mounted within valve housing 112 byconventional mounting means 121. Diaphragm 120 has a top side 122 and abottom side 124. An external spring (not shown) can be provided to biasthe diaphragm 120 into its normal static position illustrated in FIG. 3.Alternatively, the diaphragm may be formed of an elastomeric materialselected to normally retain the static position shown in FIG. 3 and todeform only under at least a predetermined pressure. Diaphragm 120defines an area designated A₁ extending to the outer periphery ofdiaphragm 120.

A plate 126 is affixed to the underside 124 of diaphragm 120. Dependingfrom the plate 126 is a rigid actuator stem 128. Mounted on actuatorstem 128 for movement therewith is a valve member 130 defining an areadesignated A₂. Valve member 130 is movable between a flow-blockingposition (shown in FIG. 3) and a flow-delivery position (shown in FIG.4).

Valve housing 112 also includes a partition or platform 132 formed toinclude an aperture 134 providing a vapor outlet. Actuator stem 128 ispositioned to extend through aperture 134. Partition 132 also provides avalve seat against which valve member 130 seats in its flow-blockingposition as shown in FIG. 3. A spring 136 or other biasing means ispositioned to act between partition 132 and plate 126. Advantageously,spring 136 normally biases valve member 130 to the flow-blockingposition blocking flow of fuel vapor from fuel tank 15 to the canisterthrough aperture 134.

Operation of the valve 110 during refueling is illustrated in FIG. 3.During refueling, it is desirable to prevent overfilling of the fueltank 15 by providing a pressurized fuel vapor barrier within the fueltank 15 which blocks the introduction of fuel in excess of apredetermined fuel capacity. Thus, during refueling, a tank pressurecontrol valve should function to prevent the escape of vapor from thefuel tank 15 by blocking off the vapor outlets.

In valve 110, vapor inlet passageway 114 is exposed to vapor pressurefrom a buildup of vapor in the fuel tank 15 as fuel is added to the tank15. Vapor pressure from the tank 15 applies a force across an area A₂ ofvalve member 130.

Second vapor inlet passageway 116 is exposed to essentially atmosphericpressure during refueling because second passageway 116 communicateswith the filler neck 117, which is uncapped and thus exposed to theatmosphere during refueling. Atmospheric pressure acts across an area A₁of diaphragm 120.

Thus, as fuel is added to the fuel tank 15 using a pump nozzle (notshown) inserted into the open filler neck 117, vapor pressure builds upto a predetermined level at which valve member 130 is biased intovapor-sealing engagement with platform 132. When valve member 130 isthus placed in the flow-blocking position, vapor is prevented fromescaping through aperture 134, and will therefore remain in the fueltank 15 to provide a pressurized vapor blanket as previously described.

Operation of the valve 110 during times other than during refueling isillustrated schematically in FIG. 4. While the vehicle is stationary orduring operation of the vehicle, it is desirable to provide head valvemeans for venting fuel vapor to a fuel vapor treatment site such as acanister to relieve pressure in the fuel tank 15. Thus, the head valvemeans should be designed to open in response to pressure in excess of apredetermined pressure to allow escape of fuel vapor from fuel tank 15through a vapor outlet.

As shown in FIG. 4, pressure relief is accomplished in valve 110 by thedeformation of diaphragm 120 in opposition to spring 136 to move thevalve member 130 away from its flow-blocking position to a flow-deliveryposition. Fuel vapor from the fuel tank 15 can vent through aperture 134and then to a vapor treatment site or the like by way of passageway 118.

Advantageously, diaphragm 120 is designed to deform at pressures inexcess of a predetermined pressure. During operation of the vehicle, topside 122 of diaphragm 120 is exposed to vapor pressure from the fueltank 15 because passageway 116 communicates with the filler neck 117 andthe filler neck 117 is capped during vehicle operation. Thus, vaporpressure from the tank applies a force across area A₂.

The underside 124 of diaphragm 120 is exposed to essentially atmosphericpressure since first outlet passageway 118 communicates with theatmosphere by way of the vapor treatment site. Thus, a pressuredifferential exists across diaphragm 120. However, diaphragm 120 isformed of sufficiently rigid material that it normally will not flexunder a pressure differential of such relatively low magnitude. Inaddition, diaphragm 120 must overcome the biasing force of spring 136 inorder to flex.

When vapor pressure builds up to a predetermined level, however, thepressure differential across diaphragm 120 increases to the point atwhich diaphragm 120 deforms in opposition to spring 136 to move valvemember 130 away from its flow-blocking position. Advantageously, area A₁is larger than area A₂. Thus, despite the fact that area A₁ and area A₂are exposed to essentially the same pressure, the force acting on areaA₁ is proportionately larger than the force acting on area A₂.

When valve member 130 has been moved to a flow-delivery position asillustrated in FIG. 4, fuel vapor can escape through aperture 134 tovent to passageway 118. Eventually, the pressure acting on area A₁ isreduced to below the predetermined level and the pressure differentialis no longer sufficient to deform diaphragm 120. At this point,diaphragm 120 returns to the static position illustrated in FIG. 3 andspring 136 supplies a restoring force to move valve member 130 back toits flow-blocking position.

Yet another embodiment of a valve in accordance with the presentinvention is illustrated in FIG. 5. In FIG. 5, reference numbersidentical to those in FIGS. 3-4 refer to features which perform the sameor similar function. In FIG. 5, a valve 210 has actuator stem 228 whichbears against a separate valve member 230 at least when the plate ismoved to a flow-delivery position. It is not necessary that actuatorstem 228 be rigidly connected to valve member 230; rather, stem 228 canbe separate of valve member 230.

In valve 210, a spring 236 seats against an interior wall 238 of housing112 and acts between interior wall 238 and valve member 230. Spring 236biases valve member 230 toward its flow-blocking position as shown inFIG. 5.

Operation of the valve 210 during refueling and during vehicle operationproceeds analogously to operation of valve 110 in FIGS. 3 and 4.

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of the invention as described and defined in thefollowing claims.

WHAT IS CLAIMED IS:
 1. An apparatus for controlling discharge of fuelvapor from a fuel tank having a filler neck, the apparatuscomprisingmeans for conducting fuel vapor between the fuel tank and afuel vapor treatment site, means for selectively blocking flow of fuelvapor through the conducting means, the blocking means being operablebetween a flow-blocking position and flow-delivery positions, means fordelivering fuel vapor from the fuel tank to the blocking means to applya closing pressure to the blocking means to assist in moving theblocking means to the flow-blocking position, and means for usingpressurized fuel vapor from the filler neck to selectively block flow offuel vapor through the delivery means so that delivery of pressurizedfuel vapor to the blocking means is controlled to control movement ofthe blocking means between the flow-blocking position and flow-deliverypositions.
 2. The apparatus of claim 1, further comprising a housingdefining an interior region, the using means being disposed within theinterior region and cooperating with the housing to define a fuel vaporflow channel in communication with the filler neck.
 3. The apparatus ofclaim 2, further comprising means for bleeding pressurized fuel vaporfrom the interior region to the fuel vapor treatment site so that theblocking means can move from its flow-blocking position to flow-deliveryposition.
 4. The apparatus of claim 2, further comprising means forventing pressurized fuel vapor from the interior region to the fuelvapor treatment site so that the blocking means can move from itsflow-blocking position to a flow-delivery position.
 5. The apparatus ofclaim 1, wherein the using means includes a diaphragm.
 6. The apparatusof claim 1, wherein the blocking means includes a diaphragm and meansfor yieldably biasing the diaphragm toward its flow-blocking position.7. The apparatus of claim 1, further comprising passageway means forconnecting the filler neck and the using means.
 8. An apparatus forcontrolling discharge of fuel vapor from a fuel tank having a fillerneck, the apparatus comprisinga housing defining an interior region andformed to include an outlet aperture, first conducting means extendingwithin the interior region for conducting fuel vapor between the fueltank and the interior region, first blocking means disposed within theinterior region for selectively blocking the flow of fuel vapor throughthe first conducting means, the first blocking means being operablebetween a closed position preventing flow from the first conductingmeans to the interior region and opened positions allowing flow from thefirst conducting means to the interior region, the first blocking meansbeing positioned to receive a closing pressure from the filler neck andan opening pressure from the first conducting means so that the firstblocking means moves to the open position when the opening pressureexceeds the closing pressure by at least a predetermined amount, secondconducting means extending within the interior region for conductingfuel vapor between the fuel tank and the outlet aperture, and secondblocking means disposed within the interior region for selectivelyblocking the flow of fuel vapor through the second conducting means, thesecond blocking means being operable between a closed positionpreventing flow of vapor through the outlet aperture and openedpositions allowing flow of vapor through the outlet aperture, the secondblocking means being positioned to receive a closing pressure from theinterior region and an opening pressure from the second conductingmeans.
 9. The apparatus of claim 8, wherein the first blocking meansincludes a diaphragm and means for yieldably biasing the diaphragmtoward the closed position.
 10. The apparatus of claim 8, wherein thesecond blocking means includes a diaphragm and means for yieldablybiasing the diaphragm toward the closed position.
 11. The apparatus ofclaim 8, wherein the first conducting means lies in fluid communicationwith the second conducting means.
 12. The apparatus of claim 8, furthercomprising passageway means for connecting the filler neck and the firstblocking means in fluid communication.
 13. The apparatus of claim 8,further comprising means for venting pressurized fuel vapor from theinterior region to the fuel vapor treatment site so that the secondblocking means may move from its flow-blocking position to itsflow-delivery position.
 14. An apparatus for controlling discharge offuel vapor from a fuel tank having a filler neck, the apparatuscomprisingmeans for conducting fuel vapor between the fuel tank and afuel vapor treatment site, means disposed in the conducting means forselectively blocking flow of fuel vapor through the conducting means,the blocking means being operable between a flow-blocking position andflow-delivery positions, means for actuating the blocking means inresponse to development of pressure of fuel vapor in the filler neck sothat the blocking means is actuated to move away from its flow-blockingposition towards its flow-delivery position allowing discharge of fuelvapor through the conducting means to the fuel vapor treatment site whenthe pressure of fuel vapor in the filler neck exceeds a predeterminedlevel, and a housing defining an interior region, the actuating meansbeing positioned in the interior region and cooperating with the housingto define a vapor flow channel in communication with the filler neck andseparate from the conducting means.
 15. An apparatus for controllingdischarge of fuel vapor from a fuel tank having a filler neck, theapparatus comprisingmeans for conducting fuel vapor between the fueltank and a fuel vapor treatment site, means disposed in the conductingmeans for selectively blocking flow of fuel vapor through the conductingmeans, the blocking means being operable between a flow-blockingposition and flow-delivery positions, means for actuating the blockingmeans in response to development of pressure of fuel vapor in the fillerneck so that the blocking means is actuated to move away from itsflow-blocking position towards its flow-delivery position allowingdischarge of fuel vapor through the conducting means to the fuel vaportreatment site when the pressure of fuel vapor in the filler neckexceeds a predetermined level, and passageway means separate from theconducting means for interconnecting the filler neck and the actuatingmeans.
 16. An apparatus for controlling discharge of fuel vapor from afuel tank having a filler neck, the apparatus comprisingmeans forconducting fuel vapor between the fuel tank and a fuel vapor treatmentsite, means disposed in the conducting means for selectively blockingflow of fuel vapor through the conducting means, the blocking meansbeing operable between a flow-blocking position and flow-deliverypositions, means for actuating the blocking means in response todevelopment of pressure of fuel vapor in the filler neck so that theblocking means is actuated to move away from its flow-blocking positiontowards its flow-delivery position allowing discharge of fuel vaporthrough the conducting means to the fuel vapor treatment site when thepressure of fuel vapor in the filler neck exceeds a predetermined level,and means for communicating an actuation signal between the filler neckand the actuating means without passing through the conducting means.17. An apparatus for controlling discharge of fuel vapor from a fueltank having a filler neck, the apparatus comprisingmeans for conductingfuel vapor between the fuel tank and a fuel vapor treatment site, meansdisposed in the conducting means for selectively blocking flow of fuelvapor through the conducting means, the blocking means being operablebetween a flow-blocking position and flow-delivery positions, and meansfor actuating the blocking means in response to development of pressureof fuel vapor in the filler neck so that the blocking means is actuatedto move away from its flow-blocking position towards its flow-deliveryposition allowing discharge of fuel vapor through the conducting meansto the fuel vapor treatment site when the pressure of fuel vapor in thefiller neck exceeds a predetermined level, the actuating means includeda diaphragm assembly situated outside of the conducting means and meansfor yieldably biasing the diaphragm assembly toward its flow-blockingposition.
 18. An apparatus for controlling discharge of fuel vapor froma fuel tank having a filler neck closable by a fuel cap engageable withthe filler neck, the apparatus comprisingmeans for conducting fuel vaporbetween the fuel tank and a fuel vapor treatment site, a diaphragmassembly situated to block flow of fuel vapor through the conductingmeans and operable between an opened position allowing flow through theconducting means and a closed position preventing flow through theconducting means, means for using pressurized fuel vapor to move thediaphragm assembly to said opened position, and means for connecting theusing means and the filler neck so that the diaphragm assembly moves tothe closed position in response to removal of the fuel cap from thefiller neck.
 19. The apparatus of claim 18, wherein the diaphragmassembly includes a diaphragm, a drive member affixed to the diaphragm,and a valve member, the drive member being positioned to bear againstthe valve member at least when the diaphragm assembly is in an openposition.
 20. The apparatus of claim 18, wherein the using meansincludes a second diaphragm assembly movable between a closed positionand opened positions and means for delivering fuel vapor from the fueltank to the second diaphragm assembly through the connecting means tomove the second diaphragm assembly to an opened position.